Physical vapor deposition (PVD) is a well known process for depositing a thin film of material on a substrate and is commonly used in the fabrication of semiconductor devices. The PVD process is carried out at high vacuum in a chamber containing a substrate (e.g., wafer) and a solid source or slab of the material to be deposited on the substrate, i.e., a PVD target. In the PVD process, the PVD target is physically converted from a solid into a vapor. The vapor of the target material is transported from the PVD target to the substrate where it is condensed on the substrate as a thin film.
There are many methods for accomplishing PVD including evaporation, e-beam evaporation, plasma spray deposition, and sputtering. Presently, sputtering is the most frequently used method for accomplishing PVD. During sputtering, a gas plasma is created in the chamber and directed to the PVD target. The plasma physically dislodges or erodes (sputters) atoms or molecules from the reaction surface of the PVD target into a vapor of the target material, as a result of collision with high-energy particles (ions) of the plasma. The vapor of sputtered atoms or molecules of the target material is transported to the substrate through a region of reduced pressure and condenses on the substrate, forming the thin film of the target material.
PVD targets have finite service lifetimes. PVD target overuse, i.e., use beyond the PVD target's service lifetime, raises reliability and safety concerns. For example, PVD target overuse can result in perforation of the PVD target and system arcing. This, in turn, may result in significant production losses, PVD system or tool damage and safety problems.
The service lifetime of a PVD target is presently determined by tracking the accumulated energy, e.g., the number of kilowatt-hours (kw-hrs), consumed by the PVD system or processing tool. The accumulated energy method, however, takes time to master and the accuracy of this method depends solely on the hands-on experience of the technician. Even when mastered, the service lifetimes of the PVD targets are still less than they could be, as approximately 20-40 percent of the PVD target (depending upon the PVD target type) is wasted. This problem is depicted in FIG. 1, which is a graph plotting the erosion profile of a conventional PVD target comprising a consumable slab of source material. As can be seen, approximately 60 percent of the original quantity of the PVD target (target residue) remained after 1769 accumulated kw-hrs of operation of the PVD process system.
The low target utilization resulting from the PVD targets' abbreviated service lifetimes, creates high PVD target consumption costs. In fact, PVD target consumption cost is one of the most significant costs in semiconductor fabrication. Thus, if much of the wasted target material could be utilized, PVD target consumption costs could be substantially reduced. This, in turn, would significantly lower semiconductor fabrication costs and increase profitability.
The low target utilization also results in more frequent replacement of the PVD target and, therefore, more frequent maintenance of the PVD system or tool. Further, when the PVD target is replaced, time is needed to retune the PVD process for the new target.
Accordingly, there is a need for an improved PVD target.